1. Field of the Invention
The present invention relates to an optical information reading apparatus, such as a raster scan type bar code reader for reading items of optical information on a plurality of parallel rows of bar codes.
2. Description of the Prior Art
Information reading apparatus such as bar code readers have been widely used in recent years as input terminals in a point-of-sale system (POS) or as terminals in an automated production control system forming a part of the factory automation (FA).
A conventional raster scan type bar code reader shown in Japanese Patent Laid-open Publication No. 63-269263 includes a vertical scanning mirror and a horizontal scanning mirror which are driven by corresponding drive mechanisms to form a raster by a scanning light beam.
Another conventional bar code reader disclosed in Japanese Patent Publication No. 1-31235 includes a rotating polygon mirror which is disposed with its axis of rotation tilted at a proper angle relative to an axis of its polygonal body. With this construction, a scanning light beam incident to the rotating polygon mirror is scanned not only in a horizontal direction but also in a vertical direction.
Both of the foregoing conventional bar code readers, however, have drawbacks described below.
The first-mentioned conventional bar code reader is complicated in construction and large in size because it requires two scanning mirrors (namely, vertical and horizontal scanning mirrors) and two drive mechanisms associated respectively therewith,
The last-mentioned conventional bar code reader in which a tilted polygon mirror is employed for bidirectional scanning has a limited number of vertical scanning lines. In the polygon mirror, each face undertakes a single scanning in the horizontal direction. To this end, each mirror face must have a certain size. Due to its peculiar polygonal shape, the polygon mirror, therefore, has a limited number of mirror faces. Due to this limited number of mirror faces, the number of the vertical scanning lines is also limited.